Stone columns are commonly installed by water jetting or air jetting cylindrical vibrating probes into the ground to form holes, which are backfilled with gravel or crushed rock densified by the vibratory probe as it is withdrawn from the ground. Water jetting is part of the vibro-flotation technology, which is often referred as vibro-replacement or wet, top feed method. Air jetting is part of the vibro-displacement or dry, top or bottom feed method. Sometimes, pre-augering is used to reduce the amount of ground displacement during the installation. The vibro-replacement method has less displacement and vibration disturbance to the surrounding ground than the vibro-displacement method, however, it has other environmental impacts due to slurry generated during the installation.
Stone columns carry more load than the surrounding soils due to their greater stiffness. Stress concentration ratio (ratio of stress carried by the column to that carried by the in-situ matrix soil) and area replacement ratio (ratio of column cross section area to total treatment area) are two key design parameters.
The typical stress concentration ratio for stone columns in weak soils ranges from 2.0 to 5.0. This technique involves the improvement of weak soils by the installation of densely compacted columns made from gravel or similar material with a vibrator. The displacement process reinforces all soils in the treatment zone and densifies surrounding granular soils.
- Reduce foundation settlement
- Increase bearing capacity, allowing reduction in footing size
- Increase stiffness
- Increase shear strength
- Reduce permeability
- Mitigate potential for liquefaction
- Permits shallow footing construction in treated fills
- Very effective for sand compaction and land reclamation
- Offers an economical alternative to piling
- A versatile ground-improvement method than can be adjusted to a wide variety of soil conditions and foundation requirements
- Can be carried out to depths of up to 15 metres
- Relatively quick execution so subsequent structural works can follow very quickly
- Enables standard shallow foundations which can lead to savings
- Environmentally-friendly as recycled materials can be used
- Extremely quiet with low vibration